Optical disk, method of manufacturing the same and optical disk apparatus

ABSTRACT

An optical disk having a data recording surface, which is prepared by the process, in which two metal molds having curvature surfaces on their cavity sides are used for making substrates having predetermined curvatures, for the optical disk by injection molding, and the substrates are adhered together such that convex surfaces of the substrates are adhered surfaces.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2000-286028, filed Sep.20, 2000, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to an optical disk from which anaccurate reproduction signal can be obtained when reproduced by a diskdrive apparatus by optimally controlling warp created in a disk-shapedrecording medium such as an optical disk or a magnetic disk, a method ofmanufacturing such an optical disk, and an optical disk device which canrecord data on such an optical disk or reproduce the data from the disk.

[0003] A disk drive device which can record data on a disk-shapedrecording medium (disk) such as CD-ROM, MO disk or DVD-disk, or canreproduce already recorded data from a disk, is connected to, forexample, a personal computer (PC), and thus used so as to supply asystem program or software for operating the PC, or for supplying andstoring a great amount of data. Alternatively, the disk drive device isconnected to, for example, a television or a monitor device, and thusused to reproduce image software or game software.

[0004] Since the first music CD was made into practical use, the memorycapacities of these disks are increased year by year.

[0005] In an optical disk of a DVD-type, a transparent resin such aspolycarbonate is used and it is formed by injection molding into asubstrate having a surface on which a record pattern is transferred anda flat mirror surface. Then, a reflection film is formed on a datarecording surface by, for example, a sputtering method. With thisstructure, a record pattern is read by making a laser beam incident onthe mirror surface.

[0006] In this case, in consideration of the productivity, substratesare, in many cases, formed in a cycle of several seconds by injectionmolding with use of a transparent resin such as polycarbonate.

[0007] However, in thin products such as substrates for optical disks,when the molding in the order of submicrons is performed in a cycle ofseveral seconds by applying such a pressure and heat for transferring adata pattern, it is not inevitable that thus produced substrates havewarps due to the remaining stress of the resin.

[0008] Nowadays, in order to further increase the density, it willbecome necessary to increase the pressure applied on a substrate and thetemperature of the resin during molding further than those in thecurrent technique as the data patter to be transferred on the substratebecomes finer, and therefore it is expected that the warp of thesubstrate will become more prominent.

[0009] Conventionally, the warp of formed substrates is controlled byadjusting the forming conditions such as the temperature of the metalmold and the pressure for tightening the mold. However, as the datapattern to be transferred on a substrate becomes finer in order toincrease the density, the degree of freedom in the forming conditions islowered. Therefore, it becomes substantially difficult to control thewarp by simply adjusting the forming conditions.

[0010] As a result, an optical disk which can be obtained by adheringsubstrates together, is warped, and thus the quality of the reproductionsignal is undesirably deteriorated.

[0011] In the meantime, when two substrates are adhered together inorder to manufacture an optical disk, it is of a general technique thatan ultraviolet curing resin is provided between substrates and made intoan adhesion layer by a spin coat method. However, in the case where thecontrol of the warp of the formed substrates is not sufficient, and thedirection of the radial warp of the substrates is unknown, it becomesdifficult to determine the conditions for applying the ultravioletcuring resin when adhering the substrates together. Thus, the unevendistribution of the ultraviolet curing resin applied and run-off of theresin are caused, thereby lowering the yield of the products.

[0012] As described above, as the density of the optical disk isincreased, the degree of freedom of the forming conditions is lowered.Therefore, it is difficult to control the warp merely by adjusting theforming conditions as in the conventional case. As a result, the warp ofthe formed substrates, which has becomes even worse, causes an adverseeffect on the adhesion of the substrates together and the reproductionof signals.

BRIEF SUMMARY OF THE INVENTION

[0013] The present invention has been proposed in consideration of theabove-described drawbacks of the conventional technique, and the objectthereof is to provide an optical disk having appropriate warp propertiesfor reproducing a signal after application of an ultraviolet curingresin for adhering two substrates and after adhering the substratestogether, an optical disks manufacturing method which can produce suchoptical disks at high yield, and an optical disk apparatus capable ofrecording data on such an optical disk and reproducing data therefrom.

[0014] According to an aspect of the present invention, there isprovided an optical disk comprising:

[0015] a data recording surface varying a state when irradiated withlight;

[0016] a first substrate for supporting the data recording surface; and

[0017] a second substrate for protecting the data recording surface,

[0018] wherein

[0019] title in a radial direction of the first and second substrates asa whole is 0.5° or more and tilt in a tangential direction is 0.10 orless.

[0020] According to another aspect of the present invention, there isprovided a method of manufacturing an optical disk having a datarecording surface, comprising the steps of:

[0021] forming a first substrate having a data recording surface byinjection molding, in which a first metal mold having a predeterminedsurface curvature in a surface on a cavity side is set to face at apredetermined distance to a second metal mold having a surface curvaturein a surface on a cavity side, which corresponds to the surfacecurvature of the first metal mold in an opposite direction, and amaterial used to form the first substrate is injected between the firstand second metal molds while a stamper holding data to be recorded inadvance on the data recording surface is provided for one of the firstand second metal molds;

[0022] forming a second substrate capable of protecting the datarecording surface of the first substrate, by injection molding, in whicha first metal mold having a predetermined surface curvature in a surfaceon a cavity side is set to face at a predetermined distance to a secondmetal mold having a surface curvature in a surface on a cavity side,which corresponds to the surface curvature of the first metal mold in anopposite direction, and a material used to form the first substrate isinjected between the first and second metal molds;

[0023] setting a predetermined amount of an ultraviolet curing resinbetween the substrates; and

[0024] adhering the two substrates together while irradiating anultraviolet ray.

[0025] According to still another aspect of the present invention, thereis provided a method of manufacturing an optical disk having a datarecording surface, comprising the steps of:

[0026] forming a first substrate having a data recording surface whichis convex with a predetermined curvature, by injection molding, in whicha first metal mold having a flat surface on a cavity side is set to faceat a predetermined distance to a second metal mold having a flat surfaceon a cavity side, the metal molds are set to have a predetermineddifference in temperature between these metal molds while a stamperholding data to be recorded in advance on the data recording surface isprovided for one of the first and second metal molds, and a materialused to form the first substrate is injected between the first andsecond metal molds;

[0027] forming a second substrate having a surface corresponding to thedata recording surface of the first substrate, which is convex with apredetermined curvature, by injection molding, in which a first metalmold having a flat surface on a cavity side is set to face at apredetermined distance to a second metal mold having a flat surface on acavity side, the metal molds are set to have a predetermined differencein temperature between these metal molds, and a material used to formthe second substrate is injected between the first and second metalmolds;

[0028] directing these substrates to an inner side such that the convexsurfaces face each other, and setting a predetermined amount of anultraviolet curing resin between the substrates; and

[0029] adhering the two substrates together while irradiating anultraviolet ray.

[0030] According to still another aspect of the present invention, thereis provided a recording apparatus capable of recording an optical diskhaving a data recording surface, obtained by adhering two substrateshaving predetermined curvatures such that convex surfaces of thesubstrates are adhered surfaces, the apparatus comprising:

[0031] a light source for irradiating light;

[0032] an optical set for guiding the light from the light sourcetowards an optical disk;

[0033] a lens for converging the light transmitted by the optical set ata predetermined position of the data recording surface of the opticaldisk, and guiding light reflected by the data recording surface to theoptical set;

[0034] a first light detector for photoelectrically converting thereflection light from the data recording surface, which is returnedthrough the optical set, and outputting a signal corresponding to adifference in distance between the lens and the data recording surfaceof the optical disk with respect to a focal distance of the lens;

[0035] a second light detector for photoelectrically converting thereflection light from the data recording surface, which is returnedthrough the optical set, and outputting a signal corresponding to adifference between a center of a light beam spot formed at a focal pointposition of the lens and a center of either one of a track and a pitline on the data recording surface of the optical disk;

[0036] a third light detector for photoelectrically converting thereflection light from the data recording surface, which is returnedthrough the optical set, and outputting a signal corresponding to adegree of tile of the data recording surface of the optical disk in aradial direction, which is created as the optical disk is rotated;

[0037] a first lens movement mechanism for moving the lens in adirection orthogonal to the data recording surface of the optical disk;

[0038] a first lens movement mechanism for moving the lens in adirection orthogonal to the data recording surface of the optical disk;

[0039] a second lens movement mechanism for moving the lens in adirection parallel to the data recording surface of the optical disksuch that the center of either one of the track and bit line coincideswith the center of the beam spot; and

[0040] a radial tilt compensation mechanism for moving the lens in adirection to cancel the tilt in the radial direction detected by thethird light detector.

[0041] According to still another aspect of the present invention, thereis provided a recording apparatus capable of recording an optical diskhaving a data recording surface, obtained by adhering two substrateshaving predetermined curvatures such that convex surfaces of thesubstrates are adhered surfaces, the apparatus comprising:

[0042] a light source for irradiating light;

[0043] an optical set for guiding the light from the light sourcetowards an optical disk;

[0044] a lens for converging the light transmitted by the optical set ata predetermined position of the data recording surface of the opticaldisk, and guiding light reflected by the data recording surface to theoptical set;

[0045] a first light detector for photoelectrically converting thereflection light from the data recording surface, which is returnedthrough the optical set, and outputting a signal corresponding to adifference in distance between the lens and the data recording surfaceof the optical disk with respect to a focal distance of the lens;

[0046] a second light detector for photoelectrically converting thereflection light from the data recording surface, which is returnedthrough the optical set, and outputting a signal corresponding to adifference between a center of a light beam spot formed at a focal pointposition of the lens and a center of either one of a track and a pitline on the data recording surface of the optical disk;

[0047] a third light detector for photoelectrically converting thereflection light from the data recording surface, which is returnedthrough the optical set, and outputting a signal corresponding to adegree of tile of the data recording surface of the optical disk in aradial direction, which is created as the optical disk is rotated;

[0048] a first lens movement mechanism for moving the lens in adirection orthogonal to the data recording surface of the optical disk;

[0049] a first lens movement mechanism for moving the lens in adirection orthogonal to the data recording surface of the optical disk;

[0050] a second lens movement mechanism for moving the lens in adirection parallel to the data recording surface of the optical disksuch that the center of either one of the track and bit line coincideswith the center of the beam spot;

[0051] a radial tilt compensation mechanism for moving the lens in adirection to cancel the tilt in the radial direction detected by thethird light detector; and

[0052] a signal reproduction mechanism for photoelectrically convertingthe reflection light from the data recording surface, which is returnedthrough the optical set, and outputting it as a signal recorded on thedata recording surface of the optical disk.

[0053] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0054] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0055]FIG. 1 is a schematic view showing an example of the optical diskmanufactured in an embodiment of the present invention;

[0056]FIG. 2 is a schematic view of an example of metal molds forforming substrates used for the optical disk shown in FIG. 1 byinjection;

[0057]FIG. 3 is a schematic view illustrating a step for adheringsubstrates formed with use of the metal molds shown in FIG. 2, with anultraviolet curing resin;

[0058]FIG. 4 is an explanatory schematic view showing an optical headdevice of an optical disk apparatus which can be used for the opticaldisk according to the embodiment shown in FIGS. 1 to 3;

[0059]FIG. 5 is a schematic diagram showing an example of a signalprocessing circuit for processing output signals outputted fromphotodiodes 106A to 106F and 106H of a light detector 106 of the opticalhead device shown in FIG. 4;

[0060]FIG. 6 is a schematic diagram showing an example of the opticaldisk manufactured by another embodiment of the present invention; and

[0061]FIG. 7 is a schematic diagram showing an example of a metal moldfor forming substrates used for a conventional optical disk, byinjection molding.

DETAILED DESCRIPTION OF THE INVENTION

[0062] An embodiment of the present invention will now be described indetail with reference to accompanying drawings. The embodiment describedbelow is merely an appropriate specific example and the scope of theinvention will not be limited by this embodiment.

[0063]FIG. 1 is a schematic diagram showing an optical disk manufacturedby the use of the embodiment of the present invention.

[0064] An optical disk 1 having a structure in which two substrates areadhered together is manufactured by the following manner. That is, asecond resin substrate 21 is adhered to one of the surfaces of a firstresin formed substrate 11 using an ultraviolet curing resin 31 as anadhesive layer. The first substrate 11 and the second substrate 21 areeach formed to have an outer diameter of 120 mm, an inner diameter of 15mm and a thickness of 0.6 mm. Further, each of the substrates 11 and 21is made of a transparent resin material (having a high transmittancerate for light having such a wavelength as of a laser beam), for thewavelength of a laser beam emitted from a semiconductor laser elementbuilt in an optical disk apparatus which will be later illustrated withreference to FIG. 5.

[0065] On the surface of the first substrate 11, with which theultraviolet curing resin 31 is brought into contact, a data recordingregion 12 and a reflection film layer 13 are laminated in the order. Itshould be noted here that the data recording region 12 is shielded fromthe outer atmosphere as it is covered by the reflection film 13.

[0066]FIG. 2 is a schematic diagram showing metal molds for injectionmolding, used to make the first and second substrates 11 and 21 shown inFIG. 1 by the injection molding.

[0067] The injection metal molds shown in FIG. 2 is made of a fixedmetal mold portion 40 and a movable metal mold portion 50, and a stamper41 is provided on the surface of the fixed metal mold portion 40, whichfaces the movable metal mold portion 50. At a predetermined position ofthe fixed metal mold portion 40, there is provided a nozzle 42 forsupplying a melted resin material supplied from a heating portion(material supply portion) which is not shown, towards the movable metalmold portion 50 at a predetermined pressure. It should be noted herethat a space 43 defined between the stamper 41 and the movable metalmold portion 50 is called cavity.

[0068] The stamper 41 of the fixed metal mold portion 40 and the surfaceof the movable metal mold portion 50, which is on the cavity 43 side,are each formed on a curved surface having a radius of curvature of 4 mor less and 2 m or more, preferably, a radius curvature of 3 m. Itshould be noted here that the direction of the curvature surface givento each respective one of the metal mold portions such that they arearranged in opposite directions to each other. In the example shown inFIG. 2, the curvature is set to have warp in such a radial directionthat is projecting towards the stamper of the fixed metal mold 40.Further, usually, as the stamper 41, a type having a pattern formedthereon to be transferred to the data recording region 12 is used toform the first substrate 11, whereas a mirror surface type stamper isused to form the second substrate 21. A method for providing a transferpattern corresponding to the data recording region 12 on the stamper 41,is as follows. First, a photoresist is applied on a glass master disk,and thus a data pattern is recorded by exposing it by a laser beam. Adeveloping process is carried out after the exposure, and thus a glassmaster disk on which recesses and projections are recorded is obtained.Next, on the glass master disk, a conductive layer is provided by, forexample, non-electrolytic plating method such as sputtering, and withuse of the conductive layer as an electrode, the stamper is formed bythe plating method. It should be noted that the material mainly used forthe stamper is Ni.

[0069] With use of the fixed metal mold portion 40 and the movable metalmold portion 50 shown in FIG. 2, the substrates 11 and 21 are thusformed. Due to the curvature surfaces provided in the metal moldportions 40 and 50, thus formed products are substrates warped in radialdirections, and therefore the most of the remaining stress in the resinwhen injection molding is released in the radial direction when thesubstrates are cooled down. Thus, the warp in the tangential directionbecomes very small. In the substrates 11 and 21 thus formed, the warp inthe radial direction is about 0.5° in the case where it is to project tothe stamper side, whereas the warp in the tangential direction is 0.1°.

[0070] The projecting surfaces of thus formed substrates 11 and 21 areboth directed to the side of the ultraviolet curing resin 31 side (theinner surface of the disk) when the optical disk 1 is formed by adheringtwo substrates together as shown in FIG. 1. During this operation, eachof the substrates 11 and 21 has a radial warp which is projecting on theadhesion surface side (that is, projection on the inner diameter sideand surface side). Therefore, the ultraviolet curing resin 31 dropped onthe inner circumferential portion in order to adhering the substratestogether, is sandwiched between both substrates as shown in FIG. 3, andthus naturally expanded towards the outer circumferential direction. Inthis manner, the ultraviolet curing resin 31 can be applied evenly tohave a uniform thickness at any coaxial positions, without creatingbubbles. After that the ultraviolet curing resin is cured by irradiatingan ultraviolet ray thereto, and thus the optical disk 1 made ofsubstrates adhered together through the ultraviolet curing resin 31serving as the adhesive layer, is obtained.

[0071] In the optical disk 1 having a structure in which two substrates11 and 21 are adhered together as above, the surface side of eachsubstrate is convex and warped in a radial direction having a radius ofcurvature of 3 m, that is, warped at about 0.5 in the radial directionand 0.1° or less in the tangential direction.

[0072] As described above, the optical disk 1 thus formed is warped in aradial direction at about 0.5°, which is relatively close to 0.8°, whichis the upper limit, whereas the warp in the tangential direction issuppressed to 0.1°or less. The upper limit of the warp in the radialdirection is 0.7° in the case where the thickness of the optical disk is0.6 mm, and it is 0.8° in the case where the thickness of the opticaldisk is 0.5 mm or less. In the meantime, the upper limit of the warp inthe tangential direction is 0.15° in the case where the thickness of theoptical disk is 0.6 mm, and it is 0.2° in the case where the thicknessof the optical disk is 0.5 mm or less.

[0073] With the above-described structure, a tangential tilt which mightnot have been eliminated completely even if a tilt compensationmechanism would be provided on the reproducing apparatus side, can bereduced to a substantially negligible level. Further, regarding theradial tile, it becomes possible to easily obtain optical disks within arange where a practical problem does not occur. It should be noted herethat the affect of the radial tilt while reproducing a signal can beeasily eliminated by providing a radial tilt compensation mechanism suchas a radial tilt servo mechanism or a cross talk canceller, in thereproducing apparatus as shown in FIG. 5. In this manner, excellentreproduction signals can be obtained.

[0074] Further, even in the case where the affect of the radial tiltbecomes significant due to a further increase in the density of theoptical disk or an enhance in NA of the objective lens, it suffices onlyif a tilt compensation mechanism in a radial direction is provided inthe reproducing apparatus. Therefore, it becomes possible to obtain goodreproduction signals with an inexpensive device.

[0075]FIG. 4 is an explanatory schematic diagram showing an optical headdevice extracted from an optical disk apparatus which can be used forthe optical disk of the embodiment of the present invention shown inFIGS. 1 to 3.

[0076] An optical head device 110 shown in FIG. 4 has a semiconductorlaser element 101 serving as a light source, in which a first laser chip101 a for outputting a first light beam LA having a wavelength of 780 nmfor a CD exclusively for reproduction, and a second laser chip 101 b foroutputting a second light beam LB having a wavelength of, for example,650 nm for a DVD-RAM which is recordable under a DVD standard, areintegrally contained, a diffraction grating 12 for impartingpredetermined diffraction properties to the first or second light beamLA or LB outputted from the semiconductor laser element 101, a hologramplat 103 for directly transmitting a light beam which has passed thediffraction grating 102, and imparting a predetermined image-formingpattern to a reflection light beam, which will be later described, acollimate lens 104 for collimating a light beam from the hologram plate103, an objective lens 105 for converging a light beam collimated by thecollimate lens 104, onto a recording surface of the optical disk 1serving as a recording medium, and a light detector 106 for detecting alight beam guided thereto after being reflected by the recording surfaceof the optical disk and its optical path being re-directed by thehologram plate 103, and outputting a voltage corresponds to the detectedlight intensity.

[0077] The optical beam having the first or second wavelength, emittedfrom the semiconductor laser element 101 passes through the diffractiongrating 102, in which predetermined diffraction properties are impartedto the beam. Then, the beam is given a predetermined image-formingpattern by the hologram plate 10, and then made incident on thecollimator lens 104.

[0078] The light beam having passed the collimator lens 104 is convertedinto a collimated light beam which is a parallel beam, and then guidedto the objective lens 105. The optical beam guided to the objective lens105 is converged by the objective lens 105 to have a beam spot of apredetermined size, and then irradiated on a pit line or a datarecording track on the optical disk 1.

[0079] The reflection light beam, which has been reflected and changedits light intensity in accordance with the presence or absence of dataon a pit line or data recording track on the recording surface of theoptical disk 1, is captured by the objective lens 105, and then inputtedthrough the collimate lens 104, where the converging properties areimparted thereto. After that, the light beam is sent back to thehologram plate 103. The reflection light beam returned to the hologramplate 103 is re-directed by the hologram plate 103, and thus the opticalpath thereof is changed towards the light detector 106.

[0080] The light detector 106, as will now be described with referenceto FIG. 5, includes 4-division photodiodes 106A, 106B, 106C and 106D fordetecting a reflection light beam of a zero-order spot generated by thediffraction grating 102, two photo diodes 106E and 106F for detectingreflection light beams of ±1-order light spot, generated by thediffraction grating 102, to which a positional relationship in adirection orthogonal to the direction in which a track is extended onthe optical disk 1 is given to detect reflection light beams by ±1-orderlight spot, and APC photodiode 106H for monitoring the intensity of thelaser beam. It should be noted that the two photodiodes 106E and 106Fare situated usually on both sides of the 4-division photodiodes 106A,106B, 106C and 106D, located at the center. The APC photodiode 106H issituated on the upstream side of the rotating direction of the opticaldisk 1 with regard to, for example, the 4-division photodiodes 106A,106B, 106C and 106D.

[0081]FIG. 5 is a schematic diagram illustrating a signal processingcircuit for processing output signals from the photodiodes 106A to 106Fand 106H of the light detector 106 of the optical head device shown inFIG. 4.

[0082] The output signals A, B, C, D, E, F, and H, outputtedrespectively from the photo diodes 106A, 106B, 106C, 106D, 106E, 106Fand 106H are amplified by amplifiers 121 a, 121 b, 121 c, 121 d, 121 e,121 f and 121 h to certain levels.

[0083] The signals A to F and H outputted respectively from theamplifiers 121 a, 121 b, 121 c, 121 d, 121 e, 121 f and 121 h areprocessed such that the signals A and B are added up by a first adder122 a, and the signals C and D are added up by a second adder 122 b. Theoutputs from these adders 122 a and 122 b are processed by a third adder123 where “(C+D) is subtracted from (A+B)”, and the resultant signal issupplied to a focus control circuit 131, as an focus error signal formaking the position of the objective lens 105 to coincide with theposition of a predetermined depth of a track or pit line of therecording surface of the optical disk and the distance where the opticalbeam converged by the objective lens 105, that is, the focal distance.

[0084] On the other hand, an adder 124 forms a signal (A+C), and anadder 125 forms a signal (B+D). These signals (A+C) and (B+D) areinputted to a phase difference detector 132. The phase differencedetector 132 is able to output a tracking error signal accurately evenin the case where the objective lens 105 is shifted, and therefore it isvery useful. Further, a reflection light beam by ±1-order light spot isconverted into a signal (E−F) by an adder 126 and supplied to a trackingcontrol circuit 133 as a tracking error signal. That is, the 0-orderlight spot and the ±1-order light spot, which are generated by thediffraction grating 101, are in a relationship in which they are shiftedby ½ track at all times while the 0-order light spot is converged on therecording track. Therefore, even if the objective lens 105 islens-shifted, the track error can be detected accurately.

[0085] Further, the signal (A+C) and the signal (B+D) are further addedup by the adder 127 and then converted into a signal (A+B+C+D), that is,a reproduction signal. After that, the signal is stored in the buffermemory 134.

[0086] On the other hand, regarding the signal H, the amount ofreflection of a light beam emitted from at least one of the first andsecond laser chips 101 a and 101 b of the semiconductor laser element 1towards the optical disk 1, on the recording surface is detected andmonitored by the APC circuit 137. In this manner, the intensity of thelight beam emitted from one of the laser chips of the semiconductorlaser element 1 is controlled to a predetermined level on the basis ofthe recording data stored in the recording data memory 136.

[0087] In the optical head apparatus having the above-described signaldetection system, when a CD disk, for example, is set on a turntable(not shown), a drive motor (not shown) is rotated at a predeterminedspeed, and at the same time, under the control of the laser drivecircuit 138, the laser beam LA of a reproduction power is irradiatedfrom the first laser chip 101 a of the semiconductor laser element 101on the recording surface of the optical disk 1.

[0088] Here, the optical head apparatus 110 is made to face acalibration area of the innermost circumference of the optical disk seton the turntable. With this structure, the reflection laser beam whichis a reflection beam of the irradiated laser beam LA is returned to thelight detector 106. The reflection light from the calibration area,which is input to the light detector 106 is converted into apredetermined electric signal by the light detector 106, and then judgedby a disk judgment circuit (not shown) if it is a CD disk.

[0089] When the type of the disk set there is detected to be a CD, thelaser beam LA having a reproduction power is continuously emitted fromthe first laser chip 101 a of the laser element 101 and a signalreproduction operation is started. Here, a detailed description of theoperation will be omitted.

[0090] When the type of the disk set there is detected to be a DVD-RAM,a laser beam LB having a reproduction power of about the same level to alower reproduction power as compared to the laser beam LB of a recordingpower is emitted from the second laser chip 111 a of the laser element101 under the control of the CPU 151. Thus, in the calibration area, therecording sensitivity of the disk is detected and the recording power ispredicted. It should be noted that when the reflection laser beam isdetected by the APC photodiode 106H, its output is reflected in theprediction.

[0091] Next, on the basis of an output from a phase shift detector 132,the deflection of the surface of the optical disk 1, that is, thedisplacement in the tangential direction of the rotation of the disk 1,is checked. Thus, the variation amount (the focus offset amount forfollow-up) of the objective lens 105 per one rotation of the opticaldisk 1, which is to be supplied to a focus coil (not shown) from thefocus control circuit 131 is set, and the objective lens 105 isfocus-locked with respect to the surface deflection of the optical disk1.

[0092] From this on, when it is detected that data to be recorded issupplied to the recording data memory 136 from outside or a buffermemory (not shown) under the control of the CPU 151, the optical headdevice 1 is moved in the radial direction of the optical disk 1 by ahead movement mechanism (not shown) while outputting the laser beam LB,so as to search a recorded region where data has been already recorded.

[0093] Next, the optical head device 101 is moved to an arbitrary trackon the optical disk 1, and the decentering of the optical disk 1 (thedisplacement in the radial direction in one rotation of the disk 1) ischecked on the basis of an output from a tracking control circuit 133and an output from the phase shift detector 132. Thus, the variationamount (the track offset amount) of the objective lens 105 per onerotation of the optical disk 1, which is to be supplied to a focus coil(not shown) from the tracking control circuit 133 is set, and theobjective lens 105 is locked with respect to the decentering of theoptical disk 1. It should be noted that as described before, the 0-orderlight spot and the ±1-order light spot, which are generated by thediffraction grating 101, are in a relationship in which they are shiftedby ½ track at all times while the 0-order light spot is converged on therecording track. Therefore, even if the objective lens 105 islens-shifted, the track error can be detected accurately.

[0094] Thereafter, the recording with the laser beam LB is continued,and the data is recorded in the order along the rotation of the opticaldisk 1.

[0095]FIG. 6 is a schematic diagram illustrating an example of adifferent optical disk from that shown in FIG. 1. It should be notedhere that the same or similar structure as or to those illustrated inFIG. 1 are designated by the same reference numerals, and detailedexplanations therefor will be omitted here.

[0096] As shown in FIG. 6, an optical disk 201 having a structure inwhich two substrates are adhered together is manufactured by thefollowing manner. That is, a second resin substrate 221 is adhered toone of the surfaces of a first resin formed substrate 211 using anultraviolet curing resin 31 as an adhesive layer.

[0097]FIG. 7 is a schematic diagram showing a flat plate metal mold forinjection molding, used to make the first and second substrates 211 and221 shown in FIG. 6 by the injection molding. The injection metal moldshown in FIG. 7 is made of a fixed metal mold portion 240 and a movablemetal mold portion 250, and a stamper 241 is provided on the surface ofthe fixed metal mold portion 240, which faces the movable metal moldportion 250. At a predetermined position of the fixed metal mold portion240, there is provided a nozzle 242. In the case where the metal moldshown in FIG. 7 is used, the stamper 241 is a mirror-surface stamper onwhich not data is recorded, and therefore it is not necessary toconsider the transfer properties. Further, the forming conditions suchas the molding temperature and the molding pressure can be setrelatively freely, and thus a substrate with no substantial warp can berelatively easily obtained.

[0098] The first substrate 211 is made of a data recording region 12 anda reflection film layer 13 which covers the entire area of the datarecording region 12, as in the case of the substrate 11 shown in FIG.11. Further, the second substrate 221 is substantially identical to thesubstrate 21 shown in FIG. 1 except only if there is warp or not.

[0099] A method of manufacturing the optical disk 201 shown in FIG. 6will now be described.

[0100] First, the first substrate 211 and the second substrate 221 areformed in an arbitrary order with use of the fixed metal mold portion240 and the movable metal mold portion 250 which constitute the flatplate metal mold. It should be noted here that a second substrate 221with no substantial warp can be obtained by setting the formingconditions such as the molding temperature and molding pressure topredetermined appropriate conditions while actually manufacturing thesubstrate. Further, for making the first substrate 211, a stamper onwhich a transfer pattern corresponding to the data recording region 12is recorded is used as the stamper 241. Here, the temperature of thefixed metal mold portion 240 which becomes a adhering surface, to whichthe stamper 241 is mounted, is set lower by about 6° C., preferably,about 4° C., as compared to the temperature of the movable metal moldportion 250.

[0101] With this structure, the substrate 211 is formed to have a statein which the adhering surface is warped to be convex due to thedifference between the resin contraction rate on the side brought intocontact with the stamper 241 and situated inner side (adhering surfaceside) while adhering the two substrates, and the resin contraction rateon the movable metal mold portion 250. When the substrate 211 is cooleddown, the contraction in the radial direction where it is convex on theadhering surface side becomes dominant, the warp created in thetangential direction can be suppressed to a very small level, that is,0.10 or less in terms of angle.

[0102] Next, the first substrate 211 and the second substrate 221 areadhered together by means of the ultraviolet curing resin 31 such thatthe data recording region 12 of the first substrate 211 is situated onan inner side. The first substrate is warped around its inner diameterside in a radial direction to be convex towards the inner surface, andtherefore the ultraviolet curing resin 31 dropped on the innercircumferential portion of the substrate 211 for spin-coat for adheringthe substrates together, can be applied on an entire surface of thesubstrate in a uniform and stable manner.

[0103] Then, with irradiation of an ultraviolet ray, the ultravioletcuring resin 31 is cured, and thus the optical disk 201 having the twosubstrates adhered together can be obtained.

[0104] In thus formed optical disk 201, the most of the remaining stressof the resin resulting in the molding can be released in the radialdirection, and therefore the warp in the tangential direction becomes0.1° or less. In other words, in the optical disk 201, the direction ofthe warp is controlled only in the radial direction, and thereforeduring the reproduction of signals, it becomes unnecessary to considerthe affect of the warp in the tangential direction whose tilt cannot beeasily compensated. Therefore, even if an inexpensive device equippedonly with a tile compensation mechanism for the radial direction is usedas the reproduction apparatus for reproducing the optical disk 201,excellent reproduction signals can be obtained.

[0105] With the disk substrates having the above-described structure,the remaining stress of the resin resulting in the formation of thesubstrates is released only in the radial direction, the warp in thetangential direction can be prevented from becoming even worse, andsuppressed to a minimum level. That is, the warp in a tangentialdirection cannot be easily eliminated by means of the tilt compensationmechanism on the disk drive side, and a substrate with theabove-described warp properties, has such a very small warpage in itstangential direction; therefore excellent reproduction signals can beobtained merely by providing a radial tilt compensation mechanism in thereproduction apparatus. In addition, its radial tilt is convex towardsthe adhering surface side, and the tangential tilt is small, andtherefore when an adhesive such as ultraviolet curing resin is appliedby a spin coat method for adhering two substrates together, it can beapplied easily on an entire surface of the substrate uniformly withoutbubbles. In this manner, it is possible to stably manufacture opticaldisks of such a good quality that the level of reproduction signals isstable and undesired noise components are not easily generated.

[0106] Further, as a means for manufacturing substrates having theabove-described warp properties in a stable and easy manner, a metalmold with a cavity, having warp in the radial direction imparted inadvance, is used. Therefore, the remaining stress of the resin in theformed substrate is released only in the radial direction, and thereforethe tangential tilt becomes small. In order to prevent the remainingstress of the resin and the radial tilt from becoming excessivelyinappropriate for adhering substrates and reproducing signals, theradius of curvature of the surface of the metal mold cavity is set to 2m or more but 4 m or less, and the direction of the surface curvature isset such that the adhering surface is convex. Within such a range of theradius of curvature, it will not drift significantly from the standardvalue of the warp in the radial direction of 0.8° for substrates of aDVD-type. Therefore, the effect of the radial tilt can be surely removedby the radial tilt compensation mechanism on the disk drive whileproducing signals. Further, as the adhering surface is set to be convex,it is possible to apply an ultrasonic curing resin used for adheringsubstrates on an entire surface of a substrate uniformly and stably.

[0107] As described above, the metal mold cavity is (made to be) warpedin a radial direction in advance. With this structure, the warp of theformed substrate can be controlled advantageously for the adhesion stepand signal reproduction. Thus, if the degree of freedom of the formingconditions is limited in accordance with a further increase in thedensity of the optical disk, the warp of the substrate can be controlledstably merely by controlling forming conditions slightly.

[0108] Further, there is a method of manufacturing a substrate, whichcan suppress the tangential tilt by relaxing in the radial direction theremaining stress of the resin within a formed substrate with certainforming conditions, for manufacturing a substrate having warp propertiesadvantageous for adhesion and signal reproduction. In this method, thetemperature of the metal mold portion which becomes a adhering surface,is set lower by about 4° C. or more, as compared to the temperature ofthe opposite metal mold portion. With this structure, the resincontraction rate on the adhering surface becomes lower, and therefore asubstrate whose adhering surface is convex can be obtained. When thesubstrate is cooled down, the contraction in the radial directionbecomes dominant, the warp created in the tangential direction can besuppressed to a very small level. The substrate thus obtained has aradial tilt which is convex to the adhering side and further a smalltangential tilt. Therefore, when such substrates are adhered together,the ultraviolet curing resin can be easily applied on an entire surfaceof the substrate in a uniform and stable manner without creating bubblesby means of a spin-coat method. Therefore, high-quality optical diskscan be manufactured stably. Further, tangential tilt, which, in somecases, cannot be completely removed by the tilt compensation mechanism,becomes small, and thus it is advantageous for reproduction of signals.

[0109] As described above, according to the present invention, excellentreproduction signals can be obtained merely by providing a radialcompensation mechanism on the reproduction device.

[0110] Further, in the adhesion step as well, it becomes possible toapply an adhesive uniformly without creating any bubbles.

[0111] In this manner, an optical disk substrate having warp propertiesadvantageously for the adhesion step and signal reproduction can beeasily obtained. Thus, if the degree of freedom of the formingconditions is limited, the warp of the substrate can be controlledstably.

[0112] Therefore, the yield of the optical disk can be improved and themanufacturing cost for the optical disk can be reduced.

[0113] Further, it becomes possible to manufacture an optical diskcapable of reproducing a signal in a stable manner at high efficiency.

[0114] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. An optical disk comprising: a data recordingsurface varying a state when irradiated with light; a first substratefor supporting the data recording surface; and a second substrate forprotecting the data recording surface, wherein title in a radialdirection of the first and second substrates as a whole is 0.5° or moreand tilt in a tangential direction is 0.1° or less.
 2. An optical diskaccording to claim 1, wherein the tilt in the radial direction is convexto an adhering direction when the second substrate is adhered.
 3. Anoptical disk according to claim 1, wherein an upper limit for the tiltin the radial direction is 0.7° when a thickness of an entire opticaldisk is 0.6 mm.
 4. An optical disk according to claim 1, wherein anupper limit for the tilt in the radial direction is 0.8° when athickness of an entire optical disk is 0.5 mm or less.
 5. An opticaldisk according to claim 1, wherein an upper limit for the tilt in thetangential direction is 0.15° when a thickness of an entire optical diskis 0.6 mm.
 6. An optical disk according to claim 1, wherein an upperlimit for the tilt in the tangential direction is 0.2° when a thicknessof an entire optical disk is 0.5 mm or less.
 7. A method ofmanufacturing an optical disk having a data recording surface,comprising the steps of: forming a first substrate having a datarecording surface by injection molding, in which a first metal moldhaving a predetermined surface curvature in a surface on a cavity sideis set to face at a predetermined distance to a second metal mold havinga surface curvature in a surface on a cavity side, which corresponds tothe surface curvature of the first metal mold in an opposite direction,and a material used to form the first substrate is injected between thefirst and second metal molds while a stamper holding data to be recordedin advance on the data recording surface is provided for one of thefirst and second metal molds; forming a second substrate capable ofprotecting the data recording surface of the first substrate, byinjection molding, in which a first metal mold having a predeterminedsurface curvature in a surface on a cavity side is set to face at apredetermined distance to a second metal mold having a surface curvaturein a surface on a cavity side, which corresponds to the surfacecurvature of the first metal mold in an opposite direction, and amaterial used to form the first substrate is injected between the firstand second metal molds; setting a predetermined amount of an ultravioletcuring resin between the substrates; and adhering the two substratestogether while irradiating an ultraviolet ray.
 8. A method ofmanufacturing an optical disk having a data recording surface, accordingto claim 7, wherein the surface curvature is 2 m or more and 4 m or lessin terms of radius of curvature.
 9. A method of manufacturing an opticaldisk having a data recording surface, according to claim 7, wherein adirection of curvature of the metal mold is convex with respect to adirection of an interface where the two substrates are adhered together.10. A method of manufacturing an optical disk having a data recordingsurface, comprising the steps of: forming a first substrate having adata recording surface which is convex with a predetermined curvature,by injection molding, in which a first metal mold having a flat surfaceon a cavity side is set to face at a predetermined distance to a secondmetal mold having a flat surface on a cavity side, the metal molds areset to have a predetermined difference in temperature between thesemetal molds while a stamper holding data to be recorded in advance onthe data recording surface is provided for one of the first and secondmetal molds, and a material used to form the first substrate is injectedbetween the first and second metal molds; forming a second substratehaving a surface corresponding to the data recording surface of thefirst substrate, which is convex with a predetermined curvature, byinjection molding, in which a first metal mold having a flat surface ona cavity side is set to face at a predetermined distance to a secondmetal mold having a flat surface on a cavity side, the metal molds areset to have a predetermined difference in temperature between thesemetal molds, and a material used to form the second substrate isinjected between the first and second metal molds; directing thesesubstrates to an inner side such that the convex surfaces face eachother, and setting a predetermined amount of an ultraviolet curing resinbetween the substrates; and adhering the two substrates together whileirradiating an ultraviolet ray.
 11. A method of manufacturing an opticaldisk having a data recording surface, according to claim 10, wherein thetemperatures of the first metal mold and the second metal mold are setsuch that the temperature of the metal mold corresponding to theinterface where the two substrates are adhered is set lower than thetemperature of the other metal mold.
 12. A method of manufacturing anoptical disk having a data recording surface, according to claim 10,wherein the difference in temperature between the first metal mold andthe second metal mold is 4° C. or more.
 13. A method of manufacturing anoptical disk having a data recording surface, according to claim 12,wherein the difference in temperature between the first metal mold andthe second metal mold is 6° C. or less.
 14. A method of manufacturing anoptical disk having a data recording surface, according to claim 10,wherein the surface curvature is 2 m or more and 4 m or less in terms ofradius of curvature.
 15. A recording apparatus capable of recording anoptical disk having a data recording surface, obtained by adhering twosubstrates having predetermined curvatures such that convex surfaces ofthe substrates are adhered surfaces, said apparatus comprising: a lightsource for irradiating light; an optical set for guiding the light fromthe light source towards an optical disk; a lens for converging thelight transmitted by the optical set at a predetermined position of thedata recording surface of the optical disk, and guiding light reflectedby the data recording surface to the optical set; a first light detectorfor photoelectrically converting the reflection light from the datarecording surface, which is returned through the optical set, andoutputting a signal corresponding to a difference in distance betweenthe lens and the data recording surface of the optical disk with respectto a focal distance of the lens; a second light detector forphotoelectrically converting the reflection light from the datarecording surface, which is returned through the optical set, andoutputting a signal corresponding to a difference between a center of alight beam spot formed at a focal point position of the lens and acenter of either one of a track and a pit line on the data recordingsurface of the optical disk; a third light detector forphotoelectrically converting the reflection light from the datarecording surface, which is returned through the optical set, andoutputting a signal corresponding to a degree of tile of the datarecording surface of the optical disk in a radial direction, which iscreated as the optical disk is rotated; a first lens movement mechanismfor moving the lens in a direction orthogonal to the data recordingsurface of the optical disk; a first lens movement mechanism for movingthe lens in a direction orthogonal to the data recording surface of theoptical disk; a second lens movement mechanism for moving the lens in adirection parallel to the data recording surface of the optical disksuch that the center of either one of the track and bit line coincideswith the center of the beam spot; and a radial tilt compensationmechanism for moving the lens in a direction to cancel the tilt in theradial direction detected by the third light detector.
 16. A recordingapparatus capable of recording an optical disk having a data recordingsurface, obtained by adhering two substrates having predeterminedcurvatures such that convex surfaces of the substrates are adheredsurfaces, said apparatus comprising: a light source for irradiatinglight; an optical set for guiding the light from the light sourcetowards an optical disk; a lens for converging the light transmitted bythe optical set at a predetermined position of the data recordingsurface of the optical disk, and guiding light reflected by the datarecording surface to the optical set; a first light detector forphotoelectrically converting the reflection light from the datarecording surface, which is returned through the optical set, andoutputting a signal corresponding to a difference in distance betweenthe lens and the data recording surface of the optical disk with respectto a focal distance of the lens; a second light detector forphotoelectrically converting the reflection light from the datarecording surface, which is returned through the optical set, andoutputting a signal corresponding to a difference between a center of alight beam spot formed at a focal point position of the lens and acenter of either one of a track and a pit line on the data recordingsurface of the optical disk; a third light detector forphotoelectrically converting the reflection light from the datarecording surface, which is returned through the optical set, andoutputting a signal corresponding to a degree of tile of the datarecording surface of the optical disk in a radial direction, which iscreated as the optical disk is rotated; a first lens movement mechanismfor moving the lens in a direction orthogonal to the data recordingsurface of the optical disk; a first lens movement mechanism for movingthe lens in a direction orthogonal to the data recording surface of theoptical disk; a second lens movement mechanism for moving the lens in adirection parallel to the data recording surface of the optical disksuch that the center of either one of the track and bit line coincideswith the center of the beam spot; a radial tilt compensation mechanismfor moving the lens in a direction to cancel the tilt in the radialdirection detected by the third light detector; and a signalreproduction mechanism for photoelectrically converting the reflectionlight from the data recording surface, which is returned through theoptical set, and outputting it as a signal recorded on the datarecording surface of the optical disk.